INVESTIGATIONS SINCE MENDEL 553 
the absence of the extra factors for size. If the tall variety is 
32 inches taller than the small variety, each of the factors A, B, 
C, and D represents 4 inches in height. Now the gametes of 
the tall variety have ABCD in them, while the corresponding 
constitution of the gametes of the small variety is abcd, and 
the fertilized eggs and first generation of hybrids resulting 
from the cross between these two varieties have the formula 
AaBbCcDd. Now since each factor for height represented by 
the large letters is responsible for 4 inches of height, the individ- 
uals of the first generation of hybrids should be 16 inches taller 
than the small variety but 16 inches shorter than the tall variety. 
They are intermediate in height between the two parents. The 
hybrids form gametes having the constitution ABCD, aBCD, 
abCD, abcD, abcd, AbCD and so on, involving all the combina- 
tions that can be made with the four pairs of letters. In fertili- 
zation all possible combinations of the various kinds of gametes 
can take place, and consequently individuals of eight various 
sizes can occur in the second generation of hybrids. Thus, if a 
gamete with a constitution abcd unites with a gamete with the 
constitution abcD, the resulting offspring has the constitution 
aabbccdD and should be 4 inches higher than the smaller variety 
of the parent generation. If a gamete with the constitution 
ABCD unites with a gamete having the constitution abCD, the 
resulting offspring, which has the factors aAbBCCDD, should 
be 24 inches higher than the smaller variety or 8 inches lower 
than the taller variety of the parent generations. It is, there- 
fore, obvious that due to the various kinds of combinations 
that may occur among the gametes, individuals of various 
sizes may occur in the second hybrid generation. 
Another peculiar situation which has been discovered among 
both plants and animals may be illustrated by the behavior of 
color in the Andalusian fowl. These fowls are what fanciers 
call blue, but when they are bred together the offspring con- 
sist of black, blue, and white fowls, and the proportion is accord- 
ing to the Mendelian ratio 1: 2:1. The black and white fowls 
breed true, but the blues breed as before. When black and 
white fowls are crossed, blue fowls are obtained. The blue is 
therefore a result of a heterozygous condition in which the 
factor for black is combined with a factor for white. In this 
case the hybrids may be regarded as having a different character 
